1. Field of the Invention
This invention pertains to a method of using a donor element in a radiation-induced thermal transfer process wherein an assemblage is provided that includes a donor element and a receiver element. The donor element has a support layer, and a transfer layer having one side adjacent the support layer and the other side adjacent the receiver element. The assemblage is then image-wise exposed to radiation whereby a portion of the transfer layer is transferred to the receiver element
2. Description of the Related Art
Imaging methods are most desirable when they produce images with sharp boundaries at the intended locations between exposed areas and unimaged areas. In radiation-induced thermal transfer imaging, especially laser-induced, boundaries between or separation of imaged and unimaged areas can be produced during or between the two steps of imaging and separation of an imageable assemblage of the donor element and the receiver element.
U.S. Pat. No. 5,935,758 “Laser induced film transfer system”, to Imation Corp. by Patel et al., discloses a procedure for imagewise transfer of a material from a donor comprising an absorber to a receptor that involves assembling the two elements in intimate face-to-face contact, e.g., by vacuum hold down or alternatively by means of the cylindrical lens apparatus described in U.S. Pat. No. 5,475,418 and scanning by a suitable laser. The assembly may be imaged by any of the commonly used lasers, depending on the absorber used, but address by near infrared emitting lasers such as diode lasers and YAG lasers, is preferred.
Any of the known scanning devices may be used, e.g., flat-bed scanners, external drum scanners, or internal drum scanners. In these devices, the assembly to be imaged is secured to the drum or bed, e.g., by vacuum hold-down, and the laser beam is focused to a spot, e.g., of about 20 micrometers diameter, on the IR-absorbing layer of the donor-receptor assembly. This spot is scanned over the entire area to be imaged while the laser output is modulated in accordance with electronically stored image information. Two or more lasers may scan different areas of the donor receptor assembly simultaneously, and if necessary, the output of two or more lasers may be combined optically into a single spot of higher intensity. Laser address is normally from the donor side, but may be from the receptor side if the receptor is transparent to the laser radiation.
Peeling apart the donor and receptor reveals a monochrome image on the receptor. The process may be repeated one or more times using donor sheets of different colors to build a multicolor image on a common receptor.
U.S. Pat. No. 5,633,113, “MASS TRANSFER IMAGING MEDIA AND METHODS OF MAKING AND USING THE SAME”, by Ernest W. Ellis to Polaroid Corporation, discloses an imaging assembly comprising a polyester enclosure or pouch having an open ended portion for receiving a donor and a receptor element. After the enclosure is loaded with the donor and receptor elements, a vacuum is drawn on both sides thereof in a vacuum chamber for evacuating the enclosure to force the donor and receptor elements into contact with each other. Once the enclosure is imaged under vacuum and opened the donor and receptor elements can be easily removed and separated since the two were held together by vacuum compression. Thereafter, the receptor can be subsequently processed such as by post-curing.
Another approach for joining the donor and receptor elements into an integral unit wherein a vacuum is maintained between the donor and receptor elements is to assemble both in a vacuum chamber, wherein they are placed in overlying face-to-face relationship with each other. After a vacuum is applied, any air existing at the interface between the donor and receptor elements will have been evacuated and the marginal edges can be sealed at to maintain the vacuum existing between the donor and receptor elements, by a suitable means, such as an adhesive layer on one or both of the mating surfaces being brought into contact with each other, as by the application of a pressure device. Following imaging the donor element, the donor/receptor elements can be separated, such as by breaking the adhesive bonding there between.
U.S. Pat. No. 6,294,308 “THERMAL IMAGING PROCESS AND PRODUCTS USING IMAGE RIGIDIFICATION” by Caspar et al. to E. I. du Pont de Nemours and Company, discloses that a laserable assemblage of a donor element that contains a thermally imageable layer, and a receiver element, is exposed imagewise so that the exposed areas of the thermally imageable layer are transferred to the receiver element in a pattern. The laser beam and the laserable assemblage are in constant motion with respect to each other, such that each minute area of the assemblage is individually addressed by the laser as necessary. This is generally accomplished by mounting the laserable assemblage on a rotatable drum. A flat bed recorder can also be used.
The next step in the process is separating the donor element from the receiver element. Usually this is done by simply peeling the two elements apart. This generally requires very little peel force, and is accomplished by simply separating the donor support from the receiver element. This can be done using any conventional separation technique and can be manual or automatic without operator intervention.
Separation results in a laser generated image, comprising the transferred exposed areas of the thermally imageable layer, being revealed on the receiver element.
U.S. 20050158652 “THERMAL IMAGING PROCESS AND PRODUCTS MADE THEREFROM”, by Jon Caspar discloses a specific method of separating an imaged laserable assemblage into a spent donor element and a receiver element, by peeling the donor element away from the nearly immobile receiver element. Peeling can be done manually, or by manipulating the donor element over a guide. A specific guide that can be used is a rod. Any direction of peeling can be used.
U.S. Pat. No. 5,578,824 by Koguchi et al. to Fuji Film Company Ltd. discloses a donor sheet having a support supporting a thin and peelable film adhered to a image-receiving material with a uniform adhesive force under heat and/or pressure that is applied by laminating means. Thermal energy is applied imagewise (e.g. by a laser) to cause imagewise reduction in the bonding force of the thin film in the donor sheet, so that the force of bond between the thin film in the donor sheet and the support becomes smaller than the force of adhesion between the thin film in the donor sheet and the image-receiving material. The donor sheet is peeled from the image-receiving material by peel/transfer means without causing uneven peeling, and the thin film which has experienced the imagewise reduction in the binding force is transferred from the donor sheet onto the image-receiving material, effecting transfer to form an image of thin-film.
The image-receiving material can be peeled from the donor sheet with pressure being applied by a pressing means such as peel rollers, whereby the non-heated area of the thin film is peeled from the image-receiving material without causing unevenness while, at the same time, the heated area of the thin film is transferred onto the image-receiving material, thereby forming an image on the latter.
The donor sheet that has a latent image formed upon exposure to an exposing head in a heating mode is peeled from the image-receiving material by a mechanism while, at the same time, the latent image on the donor sheet is developed as it is peeled by this mechanism and transferred onto the image-receiving material. The peeling mechanism can comprise a peel roller, two segmented rollers and that contact the peel roller, comb-toothed guide plates each of which is provided between segments of the rollers and along the peel roller, and a bracket in which these parts are mounted as a unitary assembly. The peel roller is axially supported by an arm and pivots about a fulcrum so that it can approach or depart from a drum holding the image-receiving material. The peel roller is also provided, via the arm, with pressing means for pressing the laminate of the image-receiving material and the donor sheet as it is carried on the drum.
The donor sheet which has a latent image formed thereon in response to the decrease in the bonding force of the thin layer as a result of the imagewise application of thermal energy due to exposure in a heating mode forms a laminate with the image-receiving material the donor sheet bonded thereto. When the arm pivots about the fulcrum so that the bracket approaches the laminate and the comb-toothed guide plates are inserted between the image-receiving layer in the image-receiving material and the thin layer in the donor sheet; at the same time, the laminate is compressed with the peel roller which is pressed against the donor sheet. If the joining length of either one of the donor sheet and the image-receiving material is made different from that of the other, the comb-toothed guide plates can be easily inserted between the two sheets. Thereafter, the drum is rotated while, at the same time, the peel roller, segmented rollers are also rotated so that the leading end of the donor sheet is moved along the comb-toothed guide plates to be held between the peel roller and each of the segmented rollers. Thus, the donor sheet is compressed with the peel roller as it is held for transport between the peel roller and each of the segmented rollers, whereby it is peeled from the image-receiving material. Thus, the donor sheet can be peeled at a constant speed in the area where it is compressed with the peel roller; as a result, the peeling force can be maintained at a constant level and neither vibrations such as “stick slip” nor uneven peel will occur. As a further advantage, the peeling force that is exerted upon the image-receiving material will not vary during the peeling operation and, hence, there will be no offset in the position where the image-receiving material is secured onto the drum, nor will there be the possibility of lower precision in registration. Thus, one can produce a monochromatic halftone image that is high in quality, resolution and contrast and which yet is free from defects such as uneven peel and failure in registration.
U.S. Pat. No. 5,695,907 “LASER ADDRESSABLE THERMAL TRANSFER IMAGING ELEMENT AND METHOD” by Jeffrey C. Chang to Minnesota Mining and Manufacturing Company discloses an imaging system including: (i) a thermal color transfer element comprising a substrate having deposited thereon in the following order; (a) a light-to-heat conversion layer; (b) a color transfer layer; and (c) a thermally transferable infrared sensitive adhesive topcoat comprising an infrared absorber and a thermoplastic material; and (ii) a receptor in intimate contact with the adhesive topcoat of the thermal transfer element.
After laser imaging the system to produce parallel but separate line images using a laser-induced thermal transfer method and separation of the receptor from the thermal color transfer element, under 200 times power microscopic examination, the resultant image on the receptor had a line width of 105 microns and a sharp line edge having no signs of fragmented patterns on either side of the imaged lines.
United States Patent Application 2006/0081332 by Tae-Min Kang, et al., titled “Laser induced thermal imaging (LITI) apparatus” discloses a laser induced thermal imaging (LITI) apparatus, a laminator, and an LITI method using the apparatus comprising: arranging a lower substrate on a chuck; arranging an upper substrate including at least a Light-to-Heat Conversion (LTHC) layer and a transfer layer such that the transfer layer faces the lower substrate; closely adhering the upper substrate to the lower substrate by raising an air pressure in a space above the upper substrate to a pressure higher than an air pressure in a space below the upper substrate; and transferring at least one portion of the transfer layer onto the lower substrate by irradiating a laser beam on the upper substrate adhered to the lower substrate. A related method further comprises providing the chuck with at least one second lower ventilation hole arranged around the lower substrate, and detaching the upper substrate from the lower substrate by injecting a compressed gas through the second lower ventilation hole after transferring the transfer layer.
U.S. Pat. No. 6,242,140 by Jang-hyuk Kwon, et al. (Jun. 5, 2001) to Samsung SDI discloses a method for manufacturing a color filter by thermal transfer using a laser beam with uniform energy distribution. The method includes forming a black matrix pattern on a substrate by photolithography.
U.S. Pat. No. 6,682,862 by Chang, et al., assigned to LG. Philips LCD Co., Ltd., titled “Method of fabricating color filter substrate for liquid crystal display device” discloses a method of fabricating a color filter substrate for a liquid crystal display device. The thermal mass transfer method includes the steps of forming a black matrix on a substrate; adhering a color transcription film to the substrate; disposing a laser head over the color transcription film; repeatedly scanning the color transcription film; and removing the color transcription film so that a color filter pattern remains in color filter pattern regions defined inside the black matrix. End lines for each one of the repeated scans are located on the black matrix.
Laser-induced mass transfer processes have the advantage of very short heating times compared to thermal printhead processes. However, the resulting images generated in the laser-induced systems can be fragmented, imperfectly resolved, of unpredictable width, or can have rough line edges. Therefore, there is a need for a thermal transfer system that takes advantage of the speed and efficiency of radiation, particularly laser, addressable systems without sacrificing image quality, resolution or line edge fidelity, without the need for special donor elements or receiver elements.